The component mounter, which mounts electric components onto a board such as a printed wiring board, optimizes an order of mounting target components in order to produce the board in the shorter period of tact time (mounting duration). As an example of this optimization method, it is suggested a method of suctioning as many components as possible at once and mounting the suctioned components onto a board using a mounting head. This method provides an order of mounting components with good production efficiency (For example, refer to Patent Reference 1: Japanese Patent Application Laid-Open Publication No. 2002-50900).
However, the conventional method of optimizing an order of mounting components determines the order of mounting components without considering a decrease in suction power of the mounting heads to suction the respective components. In other words, suction nozzles hold the components while suctioning the components in vacuum. However, for example, in the case where a diameter of a suction nozzle is too large for the size of a component, a gap appears between the component and the suction nozzle. When the gap appears, air is leaked from the gap, causing a decrease in the suction power of the suction nozzle to suction the component.
The method disclosed in the Patent Reference 1 determines an order of mounting components without considering the decrease in the suction power due to the air leakage. Therefore, there is a problem that a suctioned component may be dropped or a suction position of the component is misaligned when the mounting head moves, after a suction state of the component is recognized by a camera.
A phenomenon of dropping components due to air leakage shall be described with reference to FIG. 1 and FIG. 2.
FIG. 1 is a schematic diagram of a mounting head. A mounting head 8 includes four suction nozzles 12a to 12d. The suction nozzles 12a to 12d are connected to a vacuum room 11 which is placed in the mounting head 8. The vacuum room 11 is also connected to a vacuum generation apparatus 16, which vacuums air in the vacuum room 11 so as to make the vacuum room 11 in a vacuumed state. Accordingly, the suction nozzles 12a to 12d which are connected to the vacuum room 11 can suction respective components 14a to 14d by air-vacuum.
Furthermore, vacuum pressures necessary for suctioning the components 14a to 14d are respectively −20 kPa, −30 kPa, −15 kPa, and −20 kPa as shown in FIG. 1.
FIG. 2 is a graphic chart which shows a relationship between the number of components to be suctioned and a vacuum pressure in the vacuum room 11. Here, the vacuum pressure is a gauge pressure when an atmospheric pressure is 0 kPa. As shown in FIG. 2, when the suction nozzles 12a to 12d do not suction any components, all valves of the suction nozzles 12a to 12d are being closed. Therefore, the vacuum pressure in the vacuum room 11 is −40 kPa. On the other hand, as components are sequentially suctioned one by one, air leakage occurs due to a gap between the suctioned component and a suction nozzle. Therefore, the vacuum pressure in the vacuum room 11 is gradually increased from −40 kPa. When four components are suctioned, the vacuum pressure in the vacuum room 11 is higher than −30 kPa. In order to hold the component 14b, the vacuum pressure of less than or equal to −30 kPa is required. Consequently, the suction nozzle 12b can no longer suction the component 14b by air-vacuum, and drops the component 14b. When the component 14b is dropped, the valve of the suction nozzle 12b is kept open so that air bursts out from the suction nozzle 12b. Therefore, the vacuum pressure in the vacuum room 11 is further increased, causing the suction nozzles 12a and 12d to drop the components 14a and 14d. When the components 14 a and 14d are dropped, the vacuum pressure in the vacuum room 11 is further increased, causing the suction nozzle 12c to also drop the components 14c. As a result, all components are dropped.
Furthermore, when only three components are suctioned, the vacuum pressure indicates a value which is less than −30 kPa but closer to −30 kPa. Therefore, the suction power of the suction nozzle 12b to suction the component 14b is insufficient, causing a positional misalignment of the component 14b or a drop of the component 14b when the mounting head moves.
Note that, FIG. 3 and FIG. 4 are diagrams, each showing, for each size of a suction nozzle, a relationship between the number of components to be suctioned and a vacuum pressure in the vacuum room 11. FIG. 3 and FIG. 4 are respectively a table and a graphic chart showing the relationship. The inner diameters of suction nozzles are larger in order of SX, SA, S, and M. As shown in FIG. 3 and FIG. 4, an increase in the vacuum pressures along with an increase in the number of components to be suctioned is greater for a suction nozzle with a larger inner diameter. This is because a gap appeared between the component and the suction nozzle when the component is suctioned is greater as the inner diameter of the suction nozzle is larger.